A known reclining device of this type has a structure shown in FIGS. 1 through 3, for example. In these figures, a base plate 1 is fixed to a lower arm of a seat cushion, and a ratchet plate 5 is fixed to an upper arm of a seat back.
The ratchet plate 5 is superposed on the base plate 1 such that the ratchet plate 5 can rotate relative to the base plate 1. An operation shaft 3 positioned on the rotation center axis of the ratchet plate 5 is rotatably supported by the base plate 1 and the ratchet plate 5. A circular concavity is formed on a surface of the ratchet plate 5 opposed to the base plate 1 around the operation shaft 3. Inside teeth 7 are provided on the inner circumferential wall surface of the concavity.
Pawls 11 are provided on the concavity of the ratchet plate 5. Each of the pawls 11 has outside teeth 9 on its front end surface to engage with and disengage from the inside teeth 7 in the radial direction of the tooth end circle. Guide projections 13 and 13′ for slidingly guiding the pawls 11 in the radial direction are equipped on the base plate 1.
A cam 15 is attached to the operation shaft 3 such that the cam 15 rotates with the operation shaft 3 as one piece. The cam 15 is disposed in a space on the side of the rear end surfaces of the pawls 11. The cam 15 pushes the backs of the pawls 11 to bring the outside teeth 9 of the pawls 11 into engagement with the inside teeth 7 of the ratchet plate 5. The cam 15 engages with outer ends of spiral springs 17 engaging with the base plate 1. The spiral springs 17 urge the cam 15 in the direction of engagement between the outside teeth 9 of the pawls 11 and the inside teeth 7 of the ratchet plate 5 (locking direction).
A portion of the operation shaft 3 having an elliptical cross section is inserted through a disk-shaped release plate 21 and the cam 15. The release plate 21 is superposed on the cam 15, the pawls 11, and the guide projections 13 and 13′ in such a position as to contact one side of these components. Convexes 15a formed on the cam 15 engage with holes 21a of the release plate 21 such that the release plate 21 and the cam 15 can rotate as one piece.
Projections 11a formed on the surfaces of the pawls 11 facing to the ratchet plate 5 engage with cam grooves 21b formed on the release plate 21. The shapes of the cam grooves 21b are so determined that the cam grooves 21b shift the pawls 11 in such directions where the outside teeth 9 of the pawls 11 move away from the inside teeth 7 of the ratchet plate 5 when the release plate 21 rotates anticlockwise in FIG. 1 (for example, see Patent Reference No. 1).
Another example of known reclining device has a mechanism for separating outside teeth of pawls from inside teeth of a ratchet plate without using the release plate by a structure shown in FIG. 4. Similarly to the above example, pawls 33 are disposed between a base plate 41 and a ratchet plate 37 as apparent from the figure. The pawls 33 are guided by guide projections 45 and 45′ formed on the base plate 41 in the radial direction such that outside teeth 35 of the pawls 33 engage with and disengage from inside teeth 39 of the ratchet plate 37.
In this related-art example, grooves 33a are formed at the back of the pawls 33, and arms 31a engaging with the grooves 33a of the pawls 33 are equipped on the cam 31. In the unlocking operation, the cam 31 is rotated anticlockwise in FIG. 4. By this rotation, the outside teeth 35 of the pawls 33 are shifted in the direction where the outside teeth 35 of the pawls 33 move away from the inside teeth 39 of the ratchet plate 37 (for example, see Patent Reference No. 2).
Patent Reference No. 1: JP-A-2001-87071
Patent Reference No. 2: JP-A-2001-87069
Patent Reference No. 3: JP-A-2004-105637
Patent Reference No. 4: Japanese Patent No. 3,115,231
Patent Reference No. 5: JP-A-2002-34695
Patent Reference No. 6: JP-A-2003-180478